The Papanicolaou Cancer Research Institute has developed a transplantable, hormone responsive prostatic adenocarcinoma in rats designated as R3327. This tumor was originally found in a male Copenhagen rat by Dr. W. Dunning. We produce F1 hybrids from Copenhagen 2331 and Fischer 344 rats to use for experimental purposes. Tumor-bearing rats and unionculated controls are supplied to investigators for a variety of studies relating to prostatic cancer.